Correlation of predicted versus measured creatinine clearance values in burn patients

Four methods for predicting creatinine clearance (Ccr) from serum creatinine concentration (Scr) were evaluated in 19 male burn patients with burn wound sepsis. Measured Ccr values were calculated from 24-hour urinary catheter collections. Steady state Scr values were obtained during the same collection interval. Predicted Ccr values were derived from Scr using the methods of Cockcroft and Gault (Method II), Siersbaek-Nielsen, Kampmann and others (Method III) and Jeliffe (Methods I and IV). Wide differences between measured and predicted values were observed but were statistically significant (p less than 0.05) for Method I only. The smallest mean difference (+/-0.02 ml/min/1.73 m2) occurred with Method II measured-predicted data pairs. Method III predicted Ccr values which correlated best with measured values (r=0.770) and showed the least variability (+/-7.6 ml/min/1.73 m2). All methods appeared to overestimate when measured Ccr was less than 60 ml/min/1.73 m2. Use of estimated lean body weights did not improve correlations between predicted and measured Ccr values. While Methods II and III may provide useful initial approximations of Ccr in burn patients, reliance upon predicted Ccr values for dosage modification in burn patients may result in an insufficient reduction in dosage. Whenever possible, dosage regimens for drugs with narrow therapeutic margins should be developed or adjusted using pharmacokinetic values determined in the individual patient.